docs: def get_units(self, loss_types):
          """
          :param: a list of loss types
          :returns: an array of units as byte strings, suitable for HDF5
          """
          lst = []
          for lt in loss_types:
              if lt.endswith('_ins'):
                  lt = lt[:-4]
              if lt == 'occupants':
                  unit = 'people'
              else:
                  unit = self.units[lt]
              lst.append(encode(unit))
          return numpy.array(lst)